EXPLAINER:  MIDTERM ELECTION  ((ANIMATION W/ GFX, CAPTIONS, PHOTOS))  The U.S. holds nationwide elections every two years. Presidents serve four-year terms. The election in between is called a midterm election. Voters don’t get as excited about midterms. Participation is never as high as presidential elections. But the midterms are very important. All 435 members of the U.S. House of Representatives are up for election every two years. 1/3 of the 100-member U.S. Senate is up for election. Senators serve 6-year terms. Most U.S. states elect governors in midterm elections. Mid-terms sometimes change the political landscape. The president’s party almost always loses seats in both houses of Congress. Sometimes the loss changes the party in control of the legislature. That impacts the president’s party’s ability to pursue an agenda during the second half of his or her term.